1. Field of the Invention
The present invention relates to an optical card recording/reproducing apparatus for recording and reproducing data by using an optical card.
2. Description of the Related Art
A recent progress of technologies related to data processing is remarkable, and means for recording data with a larger capacity have been developed accordingly. As one of these means, an apparatus for optically recording and reproducing data has attracted attention.
Among other apparatuses of this sort, an optical card recording/reproducing apparatus, which uses an optical card as a recording medium and performs recording and reproduction of data-with respect to this optical card, has been put into practical use.
In this apparatus, laser beam focused by a lens is radiated on a data recording layer (light reflecting layer) of the optical card to form a pit (nonreflective portion) in the recording layer by using the resulting thermally irreversible change, thereby writing data. The optical card has a recording capacity several to ten thousand times as large as that of a conventionally used magnetic card. The memory capacity of the optical card is one to two megabytes, an extremely large value, although rewrite of data is impossible as in an optical disk. Therefore, it is possible to use the optical card in a wide variety of applications, such as a bankbook, a pocket map, and a prepaid card for use in shopping. By using the characteristic that data rewrite is impossible, it has also been attempted to use the optical card in applications, such as a private health care card, in which data must not be altered.
FIG. 1 shows an example of the optical card of the above sort. An optical recording portion 4 formed of a plurality of parallel tracks 4a is formed on the surface of an optical card 2 having a shape equivalent to that of a credit card or the like. Data can be recorded by forming data pits on these tracks 4a and reproduced by reading the data pits. The data read/write is performed by scanning a light beam emitted from an optical head (not shown) on the tracks 4a. This scan is normally done by repeatedly moving the optical card 2 in the direction of the tracks. Therefore, the scan direction during data write is sometimes opposite to that during data read. In these cases, a data string to be read out from one track is reversed in the direction of time by using a buffer memory. Consequently, data read can be performed correctly.
ID portions 6a and 6b are formed at the two ends of each track 4a. In the ID portions 6a and 6b of each track, data (ID data) indicating the track address corresponding to that track is recorded. The ID portions 6a and 6b are formed at positions inside the ends of the card by a predetermined distance (e.g., 4 mm), since the end portions of the track 4a are readily damaged or contaminated and hence are not reliable, and in order that the relative moving velocity between the optical card 2 and the optical head (light beam) in the track direction be sufficiently stabilized. A data portion 8 for recording data is formed inside the ID portions 6a and 6b. The ID portions 6a and 6b are formed on the two ends of the data portion 8 to allow read-out of the track addresses in both the directions, since the scan is performed of reciprocal movement as discussed above and reproduction is done in both the directions. Therefore, in the arrangement illustrated in FIG. 1, the ID portion 6a on the left is read when the light beam moves from the left to the right along the tracks, and the ID portion 6b on the right is read when the light beam moves from the right to the left, thereby identifying the track addresses. In this manner, the ID data can be read before the data portion 8 is read regardless of the scan direction. The data to be recorded in the ID portions 6a and 6b and in the data portion 8 is normally error-correction-coded by, e.g., Reed-Solomon product coding. This error-correction-coded data is then modulated by, e.g., 8-10 modulation and mark-length-recorded. The mark-length-recording means recording in which the length of a pit changes in accordance with recording data.
In the apparatus for performing recording and reproduction by using the optical card as described above, the position of the data portion on the optical card is predetermined. Therefore, it is important to correctly detect the positional relationship between the optical card and the optical head. This is so because the optical card is loaded on an optical card conveyor table and scanned by the optical head by reciprocally moving the conveyor table, but the optical card is not necessarily placed at the same position in each scan when loaded on the conveyor table. The position of the conveyor table can be detected by counting signals from a rotary encoder attached to a motor for moving the conveyor table. To compensate for a positional difference of the optical card from the conveyor table, however, it is necessary to detect a predetermined position on the optical card and preset a value corresponding to the predetermined position in a counter at the timing of the detection.
One example of this presetting is described in U.S. Pat. No. 4,950,876 assigned to the assignee of the present application. This USP discloses that a counter is preset when the start position of a data portion is detected. The start position of the data portion is detected only when at least one byte of data is continuously detected. However, with this technique, an erroneous value may be preset if data is not detected correctly.
Another example of the presetting is described in Japanese Patent Publication (KOKAI) No. 2-154364 (Publication date: Jun. 13, 1990) filed by the assignee of the present application. In the optical card apparatus disclosed in this publication No. 2-154364, track address data is detected from an ID portion which is read before read of a data portion, and a predetermined value is preset in a counter at the timing at which an optical head reaches the boundary between the ID portion and the data portion.
The method described in this publication, however, cannot be used for an optical card with a format in which address portions are recorded in each of ID portions in a multiple manner as mentioned below.
Recently, multiple-recording of address data (e.g., double-recording) into an ID portion has been attempted in order to ensure address data read. FIGS. 2A and 2B illustrate the ID portions 6a and 6b of a card of this type. Referring to FIGS. 2A and 2B, preamble portions 6a.sub.1 and 6b.sub.1 are formed on the left ends, and postamble portions 6a.sub.2 and 6b.sub.2 on the right ends. A fixed pattern (e.g., "101010. .") for recording a bit sync signal as a reference clock for modulated data is recorded in the preamble portions 6a.sub.1 and 6b.sub.1. Exactly the same pattern as that in the preamble portions is recorded in the postamble portions 6a.sub.2 and 6b.sub.2. A plurality of (in this example, two) address portions 6a.sub.3 and 6a.sub.4 (6b.sub.3 and 6b.sub.4) are recorded between the preamble portion and the postamble portion. Sync portions 6a.sub.5, 6a.sub.6 and 6a.sub.7 (6b.sub.5, 6b.sub.6 and 6b.sub.7) are recorded before and after these address portions. Each sync portion has a fixed pattern for recording a byte sync signal. Normally, the sync pattern is a pattern which does not violate a modulation rule but never appears in recorded data. In the address portions 6a.sub.3 and 6a.sub.4 (6b.sub.3 and 6b.sub.4), two-byte track addresses, for example, which are error-correction-coded into (6.times.5)-byte Reed-Solomon product codes and subjected to 8-10 modulation, are mark-length-recorded. The same track address data is recorded in these address portions 6a.sub.3 and 6a.sub.4 (6b.sub.3 and 6b.sub.4), and no signal for identifying these portions 6a.sub.3 and 6a.sub.4 (6b.sub.3 and 6b.sub.4) is recorded.
Assume that preset is performed of detecting the sync portions 6a.sub.5, 6a.sub.6 and 6a.sub.7 of the ID portion 6a in the above arrangement. In this case, since the patterns 6a.sub.5, 6a.sub.6 and 6a.sub.7 have precisely the same content although their positions are different, it is impossible to determine which sync pattern is detected. Consequently, an optical head and an output from a counter cannot be correctly related to each other. Likewise, since the preamble portion 6a.sub.1 and the postamble portion 6a.sub.2 have the same content although their positions are different, it is impossible to correctly relate the optical head and the counter output to each other. Furthermore, the optical head and the counter output cannot be correctly related to each other for the track address portions 6a.sub.3 and 6a.sub.4, because these address portions also have exactly the same pattern.
The data portion 8, on the other hand, can have various formats as shown in FIGS. 3A to 3C. TYPE.sub.-- A, TYPE.sub.-- B, and TYPE.sub.-- C in FIGS. 3A, 3B, and 3C are format examples in which the data portion 8 is formed of one sector, two sectors, and four sectors, respectively. In the format TYPE.sub.-- A, user data has 1,024 bytes. In the format TYPE.sub.-- B, user data has 512 bytes per sector and 512.times.2=1,024 bytes per track. In the format TYPE.sub.-- C, user data has 256 bytes per sector and 256.times.4=1,024 bytes per track.
The data portion 8 of the conventional optical card 2 can be formed of different sector types, such as TYPE.sub.-- A, TYPE.sub.-- B and TYPE.sub.-- C, in order to meet various applications. Accordingly, to meet these different sector types, it has been attempted to make it possible to select a given point as the start point of data recording/reproduction in the data portion 8 in the conventional optical card recording/reproducing apparatus.
One example of this is disclosed in the optical card recording/reproducing apparatus described in Japanese Patent Publication (KOKAI) No. 2-210617 (Publication date: Aug. 22, 1990) invented by the inventor of the present application and filed by the assignee of the present application. In this apparatus, an output from a counter for detecting the position of an optical card is compared with a reference value for representing a start point of a data sector, and, if the two values coincide with each other, it is determined that the position of the optical card is the start point of the data sector. In this arrangement, the reference value can be property switched from one value to another in accordance with a format. However, this conventional example does not refer to the presetting of the counter at all.